The present invention relates, in general, to apparatus for manufacturing liquid crystal displays (LCDs), and more particularly, to apparatus for printing bead spacers at selected locations on LCD substrates.
An LCD, which is one of the more widely used types of flat panel displays, includes two substrates, or panels, having electric field generating electrodes, i.e., pixel electrodes and a common electrode, with a liquid crystal layer interposed therebetween. The LCD displays an image by applying a voltage to the electrodes to generate an electric field in the liquid crystal layer to selectively align the molecules of the liquid crystal layer and thereby control the polarization of light passing through the layer.
Upper and lower substrates of the liquid crystal display apparatus are attached to each other by means of a sealing member formed around the respective peripheries of the substrates to confine the liquid crystal material in the space between the two substrates. The upper and lower substrates are supported relative to each other by a plurality of spacers disposed between the substrates that define and maintain a selected cell gap, or spacing, between the two substrates.
The spacers can comprise either “bead-type” spacers having a generally spherical shape, which are distributed between the substrates in a random, or irregular pattern, and columnar spacers that are distributed between the spacers in a regular pattern.
The columnar spacers are formed by coating a photosensitive film on a color filter panel of the LCD and then exposing and developing the film such that the spacers are distributed in a desired pattern corresponding to channels, gate lines, storage electrode lines, light blocking members, or other regions of the panel through which light is not transmitted. Accordingly, when columnar spacers are used in an LCD, a separate, additional photolithography process is needed, so that the production cost of the panel increases correspondingly. Additionally, unlike the plastic-based bead spacers, the columnar spacers have a relatively low elasticity, such that the margin for liquid crystal filling errors is reduced. Thus, use of columnar spacers can result in LCD panel charging problems as well as smearing of underlying layers of the panel.
On the other hand, while the irregularly distributed bead spacers do not require an additional photolithography process, the bead spacers can be located in light transmitting areas of the panel, and thus, act like extrinsic materials to cause leakage of light from the panel, thereby causing a deterioration in the light contrast of the panel. Additionally, it is possible for a portion of the bead-type spacers to move slightly during placement, and thereby cause damage to an alignment layer of the panel. Further, it is possible to inadvertently deposit the bead spacers in stacked, or double layers, such that the substrates of the LCD are spaced too far apart at some locations.
What is needed, then, is a technique that enables the less expensive bead-type spacers to be deposited on LCD substrates at precise, selected locations thereon, and which prevents the spacers from being deposited in thicknesses greater than a single layer of the spacers.